vm_backtrace.c: initialize flag

* vm_backtrace.c (rb_backtrace_print_as_bugreport): initialize
  header-printed flag.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@44699 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

vm_backtrace.c

@@ -766,7 +766,7 @@ void
 rb_backtrace_print_as_bugreport(void)
 {
     struct oldbt_arg arg;
-    int i;
+    int i = 0;
 
     arg.func = oldbt_bugreport;
     arg.data = (int *)&i;